Passive immunization of mice against Klebsiella aerogenes

Klebsiella vaccines were isolated by mild diafiltration techniques from culture filtrates of nine capsular types of K. aerogenes (K1, K2, K3, K15, K20, K35, K36, K44 & K63). The bacteria were grown in a chemically defined medium in standardized conditions in a fermenter. The vaccines had a molecular weight of more than 20 000, a carbohydrate content of 40-89%, a protein content of between less than 1 and 16% and small amounts (0.6-1.2%) of lipopolysaccharide. Antisera raised in rabbits to the nine klebsiella vaccines were standardized by passive haemagglutination, immunoglobulin G enzyme-linked immunosorbent assay and by autologous passive protection tests. Each rabbit antiserum when passively transferred to mice showed a variable capacity to passively protect mice against lethal infections by a panel of ten capsular types of K. aerogenes (K1-K10). Seven of the rabbit antisera protected mice against more than half of the challenge strains. A pool of six rabbit antisera (anti-K1, K2, K3, K20, K35 & K44) passively protected mice against lethal infections from strains of bacteria representing each of 77 capsular types of K. aerogenes.